This invention relates to vertical lift booms or jacks. More particularly, it relates to hydraulic lift booms having an external mechanical wedge lock arrangement. Extendable hydraulic lift towers are an integral part of gantry equipment employed to lift and move heavy loads. Typically, the tower comprises a series of telescoping rectangular boom segments or stages operated by one or more internal or external hydraulic cylinders.
Safety concerns dictate use of mechanical locks between boom segments to provide positive position retention to supplement the hydraulic support. Such protection is useful, for example, when a load is elevated for prolonged periods.
One arrangement, known to the industry, is illustrated in FIG. 1 There, the vertical lift mechanism 10 includes a base boom segment 12 and extendable telescoping segments 14 and 16 powered by an internal hydraulic cylinder, such as cylinder 120, illustrated in FIG. 3. Vertical hollow base 12 is of rectangular cross section and two telescoping, vertically slidable boom segments 14 and 16 extend from the base. A top platen 18 receives the load to be lifted. It is supported on a top stage boom segment 17 manually adjustable vertically relative to boom segment 16. Top stage boom segment 17 is fixed to stage 16 at adjustable vertical positions by cross rods 19. The hydraulic cylinder is internal to the base and movable segments or stages and is extendable to vertically extend boom segments 14 and 16 relative to the base 12 to lift the load on platen 18.
The lift mechanism 10 is equipped with external wedge lock mechanisms generally designated 30. Each mechanism 30 includes a pair of lock blocks 32 fixed to a rotatable shaft 34 mounted on brackets 36 supported on one of the boom segments for coaction with the next adjacent upper segment. Each shaft 34 includes a bell crank 38 connected to a horizontal hydraulic cylinder actuator 40 comprising a hydraulic cylinder 42 and actuator shaft 44. A spring 46 on each cylinder actuator urges the actuator to its extended position. When so extended, the bell cranks 38 are rotated to urge the lock blocks 32 into locking engagement with the external surface of the adjacent boom segment.
The hydraulic cylinder actuators 40 are coordinated with the lift cylinder. The lift cylinder is enabled to sustain the load on platen 18 and actually extend the telescoping boom segments a short distance vertically upward before pressurizing cylinders 42. Once pressurized, the cylinders 42 cause the cylinder actuators 40 to shorten, operating the bell cranks and causing the associated lock blocks 32 to disengage from the side walls of the adjacent boom segment. Once the blocks 32 are disengaged, the lift cylinder is caused to permit the load to descend and the telescoping booms 14 and 16 move downwardly into base 12.
While the system described above is effective and reliable, it is composed of relatively light weight shafts and linkages that must operate in the field where the equipment is subject to rough treatment.
The wedge lock system of the present invention completely eliminates the shaft and linkage components. It integrates the actuating cylinders and wedge blocks into individual enclosed assemblages. Also, as mounted on the beam segments of the lift tower, the wedge locks and operating cylinders are surrounded by protective structure reducing exposure to damage from external sources.